In U.S. Pat. No. 3,981,481 granted Sept. 21, 1976, assigned to the same assignee as the present application, a bottom operable tank car valve is disclosed including a valve body attached to an opening in the bottom of the tank. The valve body includes an opening centrally thereof for loading and unloading the lading. A depending housing is attached to the valve body with mechanical fasteners which constitute a shear plane. The housing includes a loading and unloading spout extending radially outwardly from the outlet. An operator assembly for loading and unloading the tank is mounted within a bore in the lower portion of the housing. The operating assembly includes a lower operator which extends below the valve housing and which is adapted to be engaged by a suitable unloading tool. The lower operator has a square opening engaging with clearance a square head on an upper valve operator which extends upwardly within the opening in the valve body. A retainer assembly attached to the valve body maintains the upper operator vertically fixed and spaced from the walls of the valve body. The upper operator engages a depending member from a valve closure. The closure is movable between a closed position engaging the top surface of the retainer assembly, and an open position to load or unload the lading.
The depending valve housing is a heavy and expensive member, usually a casting. If this housing could be eliminated, or made smaller, considerable cost and weight savings in the tank car valve assembly would be obtained. Also, the size and weight of this housing makes disassembly and removal of the housing awkward for the operator.
Usually the spout for unloading on the housing extends radially outwardly from the outlet only in one direction. This requires that the unloading operator move the unloading hose and connection adapter so as to engage the unloading spout in the position that the spout is located when the car arrives at destination. Since the unloading hose is often heavy and often includes little surplus length, this can be a difficult operation, and may require relocation of the tank car.
The present housing requires that the unloading hose be attached with a threaded connection. Threads are provided on the housing for attaching the unloading hose and for attaching a removable cap which is applied over the loading and unloading spout. Some receivers prefer to attach the unloading hose to the internal threads where the unloading plug is attached and where the tube for heating congealed lading is usually attached (element 104, FIG. 1 of the '481 patent). In either case attachment of the unloading hose to a threaded fitting may require the cost of the expensive plummer time in some locations to make this connection. Thus a quick-connect-disconnect connection would be more desirable than the threaded connections presently provided on the housing.
If the housing is impacted in transit, particularly adjacent the valve operator, the valve operating assembly for raising and lowering the valve closure can be damaged, making unloading difficult. Moreover if the impact is severe enough the valve closure may be moved vertically from its seated position, and if the housing shears off along the shear plane provided in the mechanical fastener, lading can escape.
In U.S. Pat. No. 4,121,614 issued Oct. 24, 1978, the depending valve housing is replaced with a depending valve guard attached to the valve body with mechanical fasteners which constitute a first shear plane. The valve guard includes a depending cylindrical portion. A valve guard cap is attached to the cylindrical portion which has a protrusion which extends outwardly below the bottom of the valve guard. The valve guard cap includes an opening located radially inwardly and preferably above the protrusion for inserting a tool to check that the valve closure is tightly engaged in the closed position, and for unloading the outlet in an emergency. Normally this opening is closed with a valve guard plug. If the valve guard assembly is impacted, little if any impact force is transmitted to the valve closure or the valve closure operator located within the valve body.
The closure operator is located within the valve body at a point above the shear plane defined by the mechanical fasteners holding the valve guard in engagement with the valve body. Thus in the event of impact to the valve guard if the impact is severe enough and has a large horizontal component, the housing will shear off along the shear plane provided in the mechanical fasteners and the valve guard assembly will drop off, leaving the closure operator and valve closure in place within the valve body. After such an impact the car can be unloaded by removing the valve guard plug and inserting a suitable fastening tool to the operator to raise the valve closure and unload the car. The valve guard cylindrical portion includes a concave contour for attachment of a bottom operable tank car valve adapter for loading and/or unloading the car.